STM8S的时钟源

单片机世界的多种时钟源

单片机的时钟源有很多种，根据其来源可将它们大致分为两类：内部时钟源和外部时钟源。而后，根据频率的不同，又可作如下划分：

内部时钟源

高速的内置时钟源 HSI
中速的内置时钟源 MSI（想到了某PC主板品牌？）
低速的内置时钟源 LSI
锁相环倍频器 PLL（和电脑CPU里的倍频系数很像）

外部时钟源

高速的外置时钟源 HSE
低速的外置时钟源 LSE

STM8S的时钟源

HSE：1~16MHz高速的外部晶体振荡器
HSE：最高16MHz的外部时钟信号
HSI：16MHz内部高速RC振荡器
LSI：128KHz的低速内部RC振荡器

上电复位后的STM8S

STM8S上电后，MCU将自动运行在HSI / 8 = 2（MHz）的时钟下。而后，你就可以随心所欲地切换时钟源，以及随心所欲地设置运行速度。

那么问题也就来了：

时钟源切换
频率设置

时钟设置代码

我自己的项目里，从没用过STM8S的LSI，所以，在代码内容中，没有LSI的切换，但我觉得可以仿照HSI的切换来编写。

新建【Drv_CLK.c】

/**
  ******************************************************************************
  * @file    Drv_CLK.c
  * @author  Elsa
  * @version V1.0.0
  * @date    5-August-2021
  * @brief   
  ******************************************************************************
  */ 
/* Includes ------------------------------------------------------------------*/
#include "Drv_CLK.h"

/* Private typedef -----------------------------------------------------------*/
/* Private define ------------------------------------------------------------*/
/* Private macro -------------------------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
/* Private function prototypes -----------------------------------------------*/
/* Private functions ---------------------------------------------------------*/
/**
  * @brief  Switch system clock to the Internal High Speed oscillator (HSI).
  * @param  HSIPrescaler : Specifies the HSI clock divider to apply.
  * This parameter can be any of the @ref CLK_Prescaler_TypeDef enumeration.
  * @param  ClockPrescaler : Specifies the HSI or CPU clock divider to apply.
  * @retval None
  */
void CLOCK_HSI(CLK_Prescaler_TypeDef HSI_PRESCALER, CLK_Prescaler_TypeDef CPU_PRESCALER)
{
  /* Enables the Internal High Speed oscillator (HSI). */
  CLK_HSICmd(ENABLE);
  /* Configures the Switch from one clock to HSI */
  while (CLK_ClockSwitchConfig(CLK_SWITCHMODE_AUTO, CLK_SOURCE_HSI, DISABLE, CLK_CURRENTCLOCKSTATE_DISABLE) != SUCCESS);
  /* Checks whether the CLK_FLAG_HSIRDY flag is set. */
  while (CLK_GetFlagStatus(CLK_FLAG_HSIRDY) == RESET);
  /* Starts manually the clock switch execution. */
  CLK_ClockSwitchCmd(ENABLE);
  /* Configures the HSI clock dividers. */
  CLK_HSIPrescalerConfig(HSI_PRESCALER);
  /* Configures the HSI and CPU clock dividers. */
  CLK_SYSCLKConfig(CPU_PRESCALER);
}

/**
  * @brief  Switch system clock to the the External High Speed oscillator (HSE).
  * @param  ClockPrescaler : Specifies the HSI or CPU clock divider to apply.
  * @retval None
  */
void CLOCK_HSE(CLK_Prescaler_TypeDef CPU_PRESCALER)
{
  /* Enable the External High Speed oscillator (HSE). */
  CLK_HSECmd(ENABLE);
  /* Configures the Switch from one clock to HSE */
  while (CLK_ClockSwitchConfig(CLK_SWITCHMODE_AUTO, CLK_SOURCE_HSE, DISABLE, CLK_CURRENTCLOCKSTATE_DISABLE) != SUCCESS);
  /* Checks whether the CLK_FLAG_HSERDY flag is set. */
  while (CLK_GetFlagStatus(CLK_FLAG_HSERDY) == RESET);
  /* Starts manually the clock switch execution. */
  CLK_ClockSwitchCmd(ENABLE);
  /* Enables the Clock Security System. */
  CLK_ClockSecuritySystemEnable();
  /* Configures the HSI and CPU clock dividers. */
  CLK_SYSCLKConfig(CPU_PRESCALER);
}

新建【Drv_CLK.h】

/**
  ******************************************************************************
  * @file    Drv_CLK.h
  * @author  Elsa
  * @version V1.0.0
  * @date    5-August-2021
  * @brief   This file contains the headers of the Drv_CLK.c
  ******************************************************************************
  */

/* Define to prevent recursive inclusion -------------------------------------*/
#ifndef __DRV_CLK_H
#define __DRV_CLK_H

/* Includes ------------------------------------------------------------------*/
#include "main.h"//This is my version of include.h

/* Exported types ------------------------------------------------------------*/
/* Exported constants --------------------------------------------------------*/
/* Exported macro ------------------------------------------------------------*/
/* Exported functions ------------------------------------------------------- */
void CLOCK_HSI(CLK_Prescaler_TypeDef HSI_PRESCALER, CLK_Prescaler_TypeDef CPU_PRESCALER);
void CLOCK_HSE(CLK_Prescaler_TypeDef CPU_PRESCALER);

#endif

修改库函数【stm8s.h】中HSE_VALUE 的值
下列代码大约从该头文件的第99行开始

/**
  * @brief  In the following line adjust the value of External High Speed oscillator (HSE)
   used in your application

   Tip: To avoid modifying this file each time you need to use different HSE, you
        can define the HSE value in your toolchain compiler preprocessor.
  */
#if !defined  HSE_Value
 #if defined (STM8S208) || defined (STM8S207) || defined (STM8S007) || defined (STM8AF52Ax) || \
     defined (STM8AF62Ax) || defined (STM8AF622x)
  #define HSE_VALUE ((uint32_t)24000000) /* Value of the External oscillator in Hz*/
 #else
  #define HSE_VALUE ((uint32_t)12000000) /* Value of the External oscillator in Hz*/	//See here
  //#define HSE_VALUE ((uint32_t)16000000) /* Value of the External oscillator in Hz*/  //See here
 #endif /* STM8S208 || STM8S207 || STM8S007 || STM8AF62Ax || STM8AF52Ax || STM8AF622x */
#endif /* HSE_Value */